System for, and method of, controlling target illumination for an imaging reader

Abstract

An imaging reader has an illuminating light assembly for illuminating a target with illumination light, and a solid-state image sensor with a rolling shutter for sequentially exposing an array of pixels to capture an image from the illuminated target. Target illumination is controlled by controlling an exposure time and a gain of the sensor, and by controlling an output power of the illumination light. The output power is maintained at a maximum level when the exposure time and/or the gain exceed a minimum threshold, and is lowered when the exposure time and/or the gain does not exceed the minimum threshold, while concomitantly maintaining the exposure time and/or the gain constant at the minimum threshold.

The invention claimed is: 
     
       1. A control system for an imaging reader having an illuminating light assembly for illuminating a target with illumination light, and a solid-state image sensor with a rolling shutter for sequentially exposing an array of pixels to capture an image from the illuminated target, the control system comprising:
 an exposure controller for controlling an exposure time of the sensor; 
 a gain controller for controlling a gain of the sensor; 
 an illumination controller for controlling an output power of the illumination light; and 
 a main controller operatively connected to the exposure, gain and illumination controllers, for maintaining the output power at a maximum level when at least one of the exposure time and the gain exceeds a minimum threshold, and for lowering the output power of the illumination light when the at least one of the exposure time and the gain does not exceed the minimum threshold, while concomitantly maintaining the at least one of the exposure time and the gain constant at the minimum threshold. 
 
     
     
       2. The system of  claim 1 , wherein the reader has a light-transmissive window relative to which the target is located in a range of working distances; and wherein the main controller lowers the output power by decreasing the output power in a direction towards the window to achieve a desired image brightness, when the at least one of the exposure time and the gain does not exceed the minimum threshold. 
     
     
       3. The system of  claim 2 , wherein the main controller maintains the output power at the maximum level when the exposure time exceeds a minimum exposure time threshold, and lowers the output power of the illumination light when the exposure time does not exceed the minimum exposure time threshold, while concomitantly maintaining the exposure time constant at the minimum exposure time threshold. 
     
     
       4. The system of  claim 3 , wherein the main controller maintains the exposure time at the minimum exposure time threshold and also maintains the gain at a minimum gain threshold, when lowering the output power. 
     
     
       5. The system of  claim 1 , wherein the main controller inversely controls the exposure time and the gain, when maintaining the output power at the maximum level. 
     
     
       6. The system of  claim 1 , wherein the main controller and the sensor are operative for determining whether ambient light substantially affects the illumination light, and wherein the main controller is operative for lowering the output power of the illumination light, and for concomitantly lowering the at least one of the exposure time and the gain, when the ambient light substantially affects the illumination light. 
     
     
       7. A method of controlling an imaging reader having an illuminating light assembly for illuminating a target with illumination light, and a solid-state image sensor with a rolling shutter for sequentially exposing an array of pixels to capture an image from the illuminated target, the method comprising:
 controlling an exposure time of the sensor; 
 controlling a gain of the sensor; 
 controlling an output power of the illumination light; 
 maintaining the output power at a maximum level when at least one of the exposure time and the gain exceeds a minimum threshold; and 
 lowering the output power of the illumination light when the at least one of the exposure time and the gain does not exceed the minimum threshold, while concomitantly maintaining the at least one of the exposure time and the gain constant at the minimum threshold. 
 
     
     
       8. The method of  claim 7 , wherein the reader has a light-transmissive window relative to which the target is located in a range of working distances; and wherein the lowering of the output power is performed by decreasing the output power in a direction towards the window to achieve a desired image brightness, when the at least one of the exposure time and the gain does not exceed the minimum threshold. 
     
     
       9. The method of  claim 8 , and maintaining the output power at the maximum level when the exposure time exceeds a minimum exposure time threshold, and lowering the output power of the illumination light when the exposure time does not exceed the minimum exposure time threshold, while concomitantly maintaining the exposure time constant at the minimum exposure time threshold. 
     
     
       10. The method of  claim 9 , and maintaining the exposure time at the minimum exposure time threshold and also maintaining the gain at a minimum gain threshold, when lowering the output power. 
     
     
       11. The method of  claim 10 , and inversely controlling the exposure time and the gain, when maintaining the output power at the maximum level. 
     
     
       12. The method of  claim 7 , and determining whether ambient light substantially affects the illumination light, and lowering the output power of the illumination light, and concomitantly lowering the at least one of the exposure time and the gain, when the ambient light substantially affects the illumination light.